Glass-to-metal seal



Sept. ,26, 1939. 1'. A. ELDER GLASS-TQ-HETAL SEAL Filed oct; 4, 1954 Fig. l-.j

Attorney.

v'in

. Patented Sept. 26, 1939 GLASS-TO-METAL SEAL Thomas A. Elder, Scotia,v N. Y., assignor to General Electric Company, a corporation o! New York Application october 4, 1934, semi No. nanos 4Claims.

The present invention relates to glass-to-metal seals.

When metal is employed as the envelope materal for electrical apparatus such as an elec- 5 trical discharge device, one of the problems en.

countered is that of passing the leading-in conductors through the metal envelope in an insulating manner. This problem is particularly diilicult in case the electric discharge device is of the power type which not only necessitates fairly high voltage between the various leading-in conductors, hencecalling for considerable insulation therebetween, but in addition, requires conductors of considerable current-carrying capacity, i.v e. of relatively large diameter.

In this connection, an important feature oi.' the invention consists in the use as one element of a sealing assembly of a tubular sleeve or eyelet having at least the surface portion thereof constituted of an alloy of nickel, cobalt and iron.

An object of the present invention is to provide an improved seal for passing relatively large leading-in conductors in an insulated'manner through metal envelopes.

Other objects and features of the invention will be apparent as the specification is perused in connection with the accompanying drawing in which Fig. 1 shows'an elevational view, partly in section, of a tube containing segeral of the improved seals and electrode supports; Figs. 2, 3, and 4 are sectional views oi modiiied forms of seals.

Referring more particularly to Fig. l, which illustrates only one of the many types of allmetalv tubes in which the improved seals may be employed to advantage, numeral I designates a cylinder consisting of any readily workable, inexpensive metal, such as iron, nickel, etc., which is closed at the .top (as shown) by a metal header member 2 and at the bottom by a metal Aheader member 3. The member I may be fabricated of the same metal as cylinder I, but the header 2 is constituted of a special alloy suitable for sealing to glass without strain, as will .be explained presently. The header members are both provided with anges which ilt snugly within the vcylinder and may be secured thereto, as by welding.

The interior assembly of the tube is illustra` tively exempliiied as taking the form of a 4electrode device having a cathode 4, an electrostatic control grid 5, a pair of screen grids 6, and an.v

' anodel. The cathode is preferably of the indirectly heated .type and is constituted of a 66 cylinderl containing a heaterinot shown) which is extended through the bottom of the cathode and connects witha leading-in conductor 8. The cathode itself is conveniently supported from the header 3 by a pair of uprights 9 which fit snugly within metal collars l0 secured respectively to the cathode and the header.

The control member 5 conveniently takes the form of a sheet metal disc, circular in shape, made of ioraminated material and mounted in a `manner described hereinafter, transverse to the longitudinal axis of the tube. The screen grids 6, also provided with perforations, areA mounted on both sides of the control member 5 and conveniently take the form of dish-shaped Y members which areilan'ged and fit snugly within the envelope, resting on. one another.

'I'he anode is constituted of a cylindrical member terminating ,at the end nearer the control member in a thick wall in which a heavy support rod -Il of copper and other suitable metal may be screwed. The other end of the anode terminates in a flange which curves inwardly, taking the form roughly of a circular section in order to eliminate or reduce the possibility of sharp edges.

Surrounding vthe support rod li there is a metal cylinder I2, the lower end of which terminates in a curved portion, similar to that provided on the anode, and the upper end has an .outwardly extending ilan'ge which is secured, as

by welding, tothe upper header member:

The anode support rod Il is insulatingly supported from the header member 2 by means of a seal improved in accordance with the present invention. For this purpose, the header 2 is first provided with an opening at the center, through which the rod passes, this opening being contained within a curved portion of the header member, indicated by reference'character i3. It is apparent that instead of forming the portion Il integral with the header 2, such portion may be made as a separate member and welded or otherwise secured to the header. Al cylinder i4 of glass provided with transverse corrugations in order to increase the insulation distance, is sealed at the lower end to the curved portion i3 of the header member and at the upper end is sealed to a metal cap I6. `'The support rod Ii is welded or otherwise secured to' the cap memsupport rod ii by means of a rod iii which is Welded or otherwise secured to the cap member it on the opposite side thereoi1 from the support rod ii.

For bringing out the various leading-in condoctors through the lower metal header l, spes cially designed seais are employed in accordance with the present invention. The seals shown by way ci example in the tube assembly or Fig. 1 involve the use of an eyelet member ill provided at one end "oi/ith an outwardly extending in order to be secured, either to the underside or the upper side oi the header member. There is a globule, bead, or cylinder i@ of or other vitreous material Within the eyelet which may support and insulate any one of the leading in conductors or support rods from the eyelet, and hence from the header member. i hermetic seal is formed between the conductor, the glass and the eyelet, preferably by means of a llame which is directed at the proper position on the eyelet after the conductor and glass members have been assembled in the eyelet. The seal, in cluoling the conductor, glass, and eyelet is cornpletecl as a apart from the header member, after which eyelet is secured, as by welding 'the header. y

it `will that the length of the glass member i8 is considerably less than the length oi the eyelet il. order to reduce any tendency for the to be deleteriously affected by the iieat generated the Weld, it is desirable to position the glass member within the eyelet as iar as possible from.' the ilanged portion of the eyelet Where 'the weld to the header member is made. i substantial space may also be left between the other end of the eyelet and the glass mass. The position of the glass member Within lthe eyelet may be predetermined by suitable and well-known fixtures and jigs on which the niembers to be sealed are assembled and heated by the gas flame referred to hereinbefore. The feature specied in the foregoing, namely, the positioning of the glass component of the seal relatively remote from the region of union of the eyelet and header member, is fully claimed in application Serial No. 240,569, November l5, i933, in the names oi? Thomas A. Elder and Albert C. Gable and assigned to the saine assignee as the present invention.

liu order to ensure o. vvacuum-'tight seal under all manufacturing and operating conditions between the glam i8, the eyelet Il and the headline-l in conductor, these members should preferably have substantially the same thermal expansion characteristic over the entire temperature range between C. and the softening temperature of the glass. An example of glms and metal which may be satisfactorily sealed under these conditions has been disclosed and claimed in the Burger and riull Patent No. 2,071,196, granted February lo, i937, and assigned to the same assignee as the present invention. The glass may consist of approximately 65% silica (S102), 23% borio oxide (B203) 7% sodium oxide (NazO) and aluminum oxide (A1203) sealed in a strainiree manner to an alloy of 18% cobalt (Co) 28% nickel (Ni) and 54% iron (Fe).

ln securing' the eyelet member l1 to the header member, it is rst necessary to provide openings in the header through which the various leadingin `conductors pass, and the flanged portion of each eyelet is then secured as by welding about each of these openings.

The conductor which passes through the glass bringing out such a conductor from the envelope upperside o`y by tlie rod spaced :from the lower l several eouidistantly pos 22, constituted or" a bioclr c i refractory insulating nia which rigid i3 are sealed at one end and secured the other end tol the electrodes U G. is therefore apparent that the control electrode is rigidly and accurately mounted r n the space contained between the screen gr .is G and yet proper provision has been made f r insulatingly bringing out a leading-in conductor from the control grid to the exterior oi' the tube.

For evacuation purposes there is provided a metal 'tabulation 2Q which is secured to the lower header and communicates through a large opening in the lower screen grid il with the upper in/ 30 terior of the tube. A pump may be attached to the lower end of the tubulation iii and when the evacuation is complete'and gas or e. source of vapor introduced, if desired, the tubulation is collapsed and welded as is disclosed and claimed in the l-Tolte application, Serial lilo. 743,832, iiled September i934, non 2,124,428 of July i9, i933, entitled Metal vacuum tube, and assigned to the same assignee as the present invention. f

The primary purpose oi the screen grids 6 is to intercept the electrostatic lines oi force which originate at the anode or the cathode and which normally would extend as far as the control inember, causing deleterious currents to iiow between the electrodes and thus aect the control normally'exercised bythe grid 5. These screening features have been disclosed and claimed in the Livingston application Serial No. 704,593, filed December 29, v1933, entitled "Electrostatically controlleol arc discharge device," assigned to the same assignee as the present invention. This application has matured into Letters Patent No. 2,044,618.

Instead of employing` the eyelet form of seal for carrying tlie'conductors 8 and i9 through the lower header member, it may be desirable to use any one of the seal constructions shown in Figs.

Eil

2, 3 and 4. In Fig. 2, reference character 3G refers to a portion of a metal container which may, for 00 example, comprise either of the header members 2, 3er the container I illustrated in Fig. 1. A leading-in conductor or electrode support is designated by the reference character 3|. For

in an insulating manner, the container or header 30 is first' provided with an opening 32 large enough to provide a suilicient space about the conductor 3|. Secured to the member 30 as by' welding, there `is a cylinder 33, made oi' iron or nickel and having an outwardly extending flange 34 on one end and an inwardly extending flange 35 on the other end. This cylinder is also provided with a. relatively large opening 36 through which the conductor passes. Resting on the cyl- 75 inder and secured thereto as by welding, there is a heavy metal washer I1 which is preferably constituted of a special alloy. A cylinder of glass 1 Il is butt-sealed to the upper surface of the washerandisalsosealedatitsuppsrendtoa cap member II provided with a flange for sealing purposes. Therodli maybeweldedtotheinterior surface of the cap member, which carries -mitsexteriorsurfacearodliitoserveasa terminal for the rod il.

Thecapmember andtheheavywasherl arepreferablyconstitutedofametalwhichhas substantially the same thermal expansion characteristicastheglasscylinderllatalltemperaturesfrom 0 C. upto andincludingthesoftening temperature of-the glass. Examples of such materials are given hereinbefore.

Asealofthischaractermaybemadeforvarious voltages by increasing or tbe length of the glass cylinder Il. In addition, it is possible to utilize a metal for'the cylinder 38 whichmaybemore easilydrawnandislessexpensive than the metal of which washer Il is composed. Thusasealofthistypemaybe cheaply fabricated and .the minimum amoimt of alloy having the proper thermal expansion characteristic required, yet an eflective seal is obtained for bringing out conductors of all sises. large and small, from the interior of the metal container to the exterior thereof.

InFig.3. the seal issomewhat similartothat shown in Fig. 2 so that corresponding elements have been given the same reference characters,

.except that the glass cylinder n is now buttsealed to the ilan cylinder Il constituted of the special alloy. e cylinder Il may be made ofstockdrawntoshapeandutilizlngtheminimum quantity of alloy. This cylinder is preferably welded or otherwise secured to the heavy washer I2 which may be constituted of an inexpensive metal and which in turn is welded or otherwise secured to the member Il, which forms part of the metal envelope. Heavy washer 42 prevents transmission of strains from member 3l tomemberll andtheresultisasavinginthe amount of special alloy required for member 4I.

Pig. 4 shows a stili diilerent form of seal for carrying a combined leading-in conductor and Support wire li through a portion $0 of a metal container in an insulating manner. Secured to the member. Iii there is a flanged cylindrical member il. This cylinder contains a cylinder 4I, to which it is welded. leavingl an annular space therebetween for receiving one end of the glass cylinder ll.- The cylinder Il is sealed toeachmetal cylinder. Theupper end ci the glasscylinder Ilissledontheintexicntoa metalcylindcrll.whiletotheexteriorsurface oftheglassc'yiiliderthereisseaiedametalein memherl'l. 'Ihesupportrodllisweldedto thecspmember and, lfdcaired,anadditionalrod gemwmaybcweldedtotheuppersideofthecap 'rnc cylinders as, u, u, ma I1 are preferably constituted of a special alloy having substantialcharactexistic as joint is formed between contiguous peridssral surfaces of the joined cylindricaimembers. Thus larger insulating surfaces are offered between the metal and glass which provides greater rnechanical strength and also greater tol s leaks along tbeglass and metal boundary.

AsinthecaseofthesealsshowninFlLLthe sealsillustratedinli'igs.2,3,and4maybemade by automatic machinery, on a quantity production basis, complete in themselves and apart fromthemetalheaderorothermetalportion of theenvelope. Thesealsmaybereadilysecured to the envelope. By separating the operations ofthesealasmuchaapossiblefromtheoperations performed on the metal envelope. as for example, assembling and securing the screen grids l and the controlgrid i within the envelope, it is apparent that work on the tube as awholecanprogressmuchfasterthanif the fabrication of the seals were intimately tied up an with operations on the envelope. Furthermore. when the seals are formed separate from the envelope in the manner described hereinbefore. any damage'to the'seais during fabrication causes the scrapping only of the seal in question and 25 does not involve the remainder of the tube.

It is apparent that while I have described the various seals as being and fabricated apart from the envelope, thereafter, secured thereto, it will be understood that if desired, the 30 seals may be built up, piece by piece. directly on the envelope, although auch a procedure is not preferred.

What-Iclaimasnew and desire'tosecureby letters Patent of the United States, is:

1.` In combination with a metallic container, a metallic tubular projection from the wall thereof, an electrical conductor passing through said tubular projection and separated from the walls thereof by glass fused vacuum-tight to said projection and said conductoythe surface of said projection to which said fusion is made being of an alloy of nickel, cobalt and iron.

2. In combination with a metallic container, a metallic tubular projection from the wall thereof, an electrical conductor passing through said tubular projection and separated from the walls thereof by glass fused vacuum-tight to said pro- .iection and said conductor, the surface of said projection and said conductor to which said fusion is made being of an alloy of nickel, cobalt and iron.

3. In combination with a metallic container. a

alloyof nickel, cobalt and iron. an annular sleeve havingatleastits surfacelayerofanalloyof nickel, cobalt and iron surrounding it and in- 

